An incident was generated from an MS Excel file with Credit Card numbers, but when you search the file, the flagged numbers seem to not exist.
To find the number, verify first that no filter is applied to the Workbook and there is no special formatting. If yes, then remove the filter and possibly any format which might not display the number properly. After completing this, you will be able to search and find the matched credit card numbers flagged in the incident report.
Although this issue was seen with Credit Card number, this can apply to any sensitive data with digits numbers.